Recently, the widespread use of the Internet makes content distribution more popular where content, including moving pictures and audios, is distributed and played back via an IP (Internet Protocol) network. In the distribution of this kind, in order to improve the transmission efficiency of for example moving pictures, highly efficient compression encoding scheme based on the inter-frame prediction is used in many cases. In those schemes, predictive parameters, acquired by predicting the encoded images from the temporally preceding and following frames, and predictive residual image data are encoded to reduce the amount information of temporally correlated moving picture data. In addition, the high compression and encoding of predictive residual image data through transform-coding and quantization enables content data to be transmitted using a small amount of transmission bandwidth.
Typical exemplary transmissions use compression and encoding schemes such as MPEG (Moving Picture Experts Group)-1, MPEG-2, and MPEG-4. In those compression encoding schemes, inter-frame prediction is performed for an input image frame for each fixed-size rectangular area, called a macro block, through motion compensation, and the obtained motion vectors and the signal data, generated by compressing the predictive residual image data through the two-dimensional discrete cosine transform and quantization, are variable-length coded.
Effective compression encoding schemes based on the inter-frame prediction, such as AAC (Advanced Audio Codec), are also available for audios to enable content distribution that uses the transmission bandwidth efficiently.
As a file format for recording these content data, the file format such as an MP4 file format or a 3GP file format is present. These can record a plurality of media, encoded data with a distribution rate (compression rate), and a distribution encoded data unit.
There are a lot of methods of distributing encoded data of such a content over an IP (Internet Protocol) network that uses a packet switching system. It is considered that this distribution will be expanded in the future to perform content distribution in a mobile communication system in which a mobile station constituted from a PHS (Personal Handyphone System), a cellular phone, or a portable terminal that uses these as communication means is connected to a wireless base station through a wireless channel.
Patent Document 1 described below discloses a configuration including N transmission means for converting audio data to N encoded data and transmitting the encoded data to M transmission paths at a constant interval or an adaptively changing time interval. In this configuration, selection of a transmission path is made by a selection unit and the encoded data is selected from among the encoded data that could be normally received, for reconstruction by an encoding data reconstruction unit.    Non-patent Document 1: Schulzrinne, H., Rao, A., Lanphier, R, “Real Time Streaming Protocol (RTSP)”, RFC 2326, April 1998, Internet URL address <http://www.ietf.org/rfc/rfc2326.txt obtained from http://www.ietf.org/>    Non-patent Document 2: Handley, M., Jacobson, V., “SDP: Session Description Protocol”, RFC 2327, April 1998, Internet URL <http://www.ietf.org/rfc/rfc2327.txt obtained from http://www.ietf.org/>    Non-patent Document 3: Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, “RTP: A Transport Protocol for Real-Time Applications”, RFC 1889, January 1996, 5.1 RTP Fixed Header Fields. Internet URL <http://www.ietf.org/rfc/rfc1889.txt obtained from http://www.ietf.org/>    Patent Document 1: JP Patent Kokai Publication No. JP-P-2003-318851A (Page Nos. 14 and 15, FIG. 1)